This invention relates to three-dimensional displays, and more particularly to volumetric three-dimensional displays.
Volumetric displays are a class of three-dimensional display technology that produce volume-filling imagery. Typically, volumetric displays are autostereoscopic; that is, they produce imagery that appears three-dimensional without the use of additional eyewear.
Some volumetric displays create three-dimensional imagery by employing spatio-temporal multiplexing in emitting or scattering light from a range of locations within an image volume. In other words, a smaller number of light-generating devices (for example, lasers, projector pixels, etc.) are run at a higher frequency than an overall volumetric refresh rate, and the light is imaged onto a rotating surface. Persistence of vision integrates the image slices formed at different spatio-temporal locations of the volume swept by the rotating surface, and the viewer perceives a volume-filling, three-dimensional image.
The concept of a volumetric display in which three-dimensional imagery is perceived by visual integration of a series of images projected on a rotating screen has existed since, at least, the late 1950s. In 1958, Max Hirsch filed a patent application for a xe2x80x9cgenerescope,xe2x80x9d wherein imagery formed on the surface of a cathode ray tube (CRT) is relayed by a periscope-like arrangement that images onto a rear-projection screen. In the generescope, the CRT, mirrors, and screen rotated in unison. The arrangement of rotating relay mirrors keeps the projection optical path length invariant with respect to the projection screen angle. For this, Hirsch was issued U.S. Pat. No. 2,967,905 in 1961.
A 1960 Aviation Week article entitled xe2x80x9cNew Display Gives Realistic 3-D Effect,xe2x80x9d (pp. 66-67, Oct. 31, 1960) describes a 3-D display developed by ITT Laboratories. It is similar to the display taught by Hirsch, in that a sequence of 2-D images formed on the surface of a CRT are relayed to a rotating projection screen by an arrangement of mirrors that rotate with the projection screen, thereby keeping the projection optical path length invariant with respect to the projection screen angle. However, the ITT display employs a stationary CRT and front-end optical components. One consequence of their architecture is that the CRT""s image rotates in the plane of the projection screen as the projection screen rotates.
Other volumetric displays which employ similar radially-extended relay optics include the volumetric displays described by Batchko (U.S. Pat. No. 5,148,310) and Tsao et al. (U.S. Pat. Nos. 5,754,147 and 5,954,414). Batchko describes a volumetric display wherein a rotating screen is illuminated by a fixed, vector-scanned laser illumination source. Tsao and co-workers utilize a k-mirror system, which rotates at half of the screen""s angular frequency, to prevent the image of the projector from rotating in the plane of the projection screen.
The invention features systems and methods for producing three-dimensional volume-filling imagery. A volumetric display system produces a volume image by projecting a series of two-dimensional images onto a rapidly rotating projection screen. Persistence of the human visual system integrates these two-dimensional image slices into a three-dimensional volume-filling image.
In general, in one aspect, the invention features a volumetric display system including an optical relay, a motor, a support structure coupled to the motor, a projection screen positioned on the support structure, and a projection optic. During operation, the projection optic receives a light beam from the optical relay and projects the light beam onto the projection screen. Also, the motor rotates the support structure, the projection screen, and the projection optic about a rotation axis.
Embodiments of the display system may include any of the following features.
The display system may further include having the projection optic positioned on the rotation axis.
The projection optic may also be a projection lens. In some embodiments, the projection lens has a lens axis, and the lens axis and the rotation axis define an angle of no more than about 10 degrees. Moreover, the angle may between about 4.9 degrees and 5.0 degrees. The projection lens may be a triplet lens.
The display system may further include having the projection screen, defining a plane, positioned on the support structure so that the rotation axis lies in the plane defined by the screen.
The system may still further include a first and second mirror placed on the support structure. During operation, the motor rotates the first and second mirrors about the rotation axis. Also, the first mirror receives the light beam from the projection optic and directs the light beam to the second mirror, and the second mirror directs the light beam to the projection screen.
The system may additionally include a third mirror placed on the support structure. During operation the motor also rotates the third mirror about the rotation axis, and the third mirror receives the light beam from the second mirror and directs the light beam to the projection screen.
In some embodiments, the support structure may be a platform having a hole, and the projection lens may be mounted within the hole.
Also, the optical relay may include a relay lens and a field lens. During operation the relay lens can receive the light beam from a light source and relay the light beam to the field lens, and the field lens relays the light beam to the projection lens.
In general, in another aspect, the invention includes a method of producing volume-filling imagery. The method includes: (i) rotating a projection optic and a projection screen about a rotation axis; (ii) supplying a light beam from a stationary light source; and (iii) projecting the light beam through the projection optic onto the projection screen.
Embodiments of the method may further include any of the following features.
The projection optic may be a projection lens having a lens axis, and the method further includes tilting the projection lens so that the lens axis defines an angle with the rotation axis, the angle being no more than about 10 degrees.
The method may also include rotating a first and second mirror about the rotation axis. Furthermore, the projection optic may project the light beam onto the first mirror, the first mirror may direct the light beam onto the second mirror, and the second mirror may direct the light beam onto the projection screen.
Some embodiments may further include rotating a third mirror about the rotation axis. The third mirror may receive the light beam from the second mirror and may direct the light beam onto the projection screen.
In some embodiments, the method further includes directing the light beam from the light source onto the projection optic using an optical relay. Furthermore, the optical relay may include a mirror, and the method may include adjusting the mirror to center the light beam on the projection screen.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.